The present invention is generally related to radio control techniques, and, more particularly, to method and computer-readable medium configured to control signaling and channel assignment in a decentralized trunked radio system to operationally mimic a centralized trunked radio system.
In a conventional (non-trunked) radio system, a radio can generally access only one channel at a time. If that channel is in use, the user must either wait for the channel to become idle or manually search for a free channel. A trunked radio system differs from a conventional system by having the ability to automatically search all available channels for one that is clear. In the United States, the Federal Communications Commission (FCC) has recognized at least two main types of trunking: centralized and decentralized. A centralized trunked system uses one or more control channels to transmit channel assignment information to the mobile radios. In a decentralized trunked system, the mobile radios scan the available channels to find one that is clear. The rules require that licensees take reasonable precautions to avoid causing harmful interference, including monitoring the transmitting frequency for communications in progress. This requirement is met in decentralized trunked systems because each mobile unit monitors each channel and finds a clear one to transmit on. In a centralized trunked radio system, radios typically monitor the control channel(s), not the specific transmit frequencies. Therefore, this form of trunking has not, generally, been allowed in the shared bands, typically below 800 MHz.
In view of the foregoing, users of Specialized Mobile Radios (SMRs),—also generally known as LMR (Land Mobile Radio), PAMR (Public Access Mobile Radio), PMR (Private Mobile Radio), TMR (Trunked Mobile Radio), TRS (Trunked Radio System), etc.—that share a plurality of non-exclusive radio channels (shared bands) have been unable to take advantage of digitally addressed trunked systems due to such regulatory requirements, generally referred to as de-centralized operation requirements. Decentralized operation commonly requires that: a) each channel must be available for all users licensed on a particular frequency, effectively prohibiting use of a dedicated control channel; and b) each channel must be monitored and determined as available before being used. In practice, the users of these channels have been forced to remain with older technologies, not utilizing a dedicated-control channel, with concomitant lower efficiency and limited functionality.
One known solution is to provide a scan function in the user terminals combined with analog tone signaling on the repeaters. For example, the radios constantly search the pre-programmed frequencies for signaling they are programmed to respond to. A variety of different signaling schemes has been used in the past: Improved Mobile Telephone System (IMTS), GE-MarcV radio system, Dual Tone Multiple frequency (DTMF), five-tone schemes, and others. Unfortunately, such schemes are generally based on primitive analog signaling, resulting in slow access time and rudimentary functionality when compared to presently available digitally signaled trunked systems with control channel functionality, such as provided by the EDACS® radio system, purveyed by the assignee of the present invention.
Thus, it would be desirable to provide system and techniques that can accommodate an ever-increasing number of users on limited shared bands while providing such users with improved features commonly available to users of trunked radio systems in frequency ranges not subject to shared channel operation restrictions. It would be further desirable to provide digital signaling that essentially mimics a centralized control channel operation and can be cycled among all channels in the system, meeting both the intent and the letter of existing governmental regulations.